Burst fire mechanism for auto-loading firearm

ABSTRACT

An auto-loading firearm that may be fired semi-automatically and fully automatically is provided with a firing mechanism that permits bursts of, say, three rounds to be fired each time the trigger is pulled. The mechanism comprises a secondary sear disengager and interrupter support member pivotally mounted on the frame of the firearm so that upward movement of the forward end of the support member will cause the upper end of the secondary sear to move rearwardly out of engagement with the secondary sear notch of the hammer. An automatic fire activator link is pivotally mounted on an activator link positioner which, in turn, is pivotally mounted on the frame. The activator link positioner and the activator link are longitudinally movable to a rearwardmost, to an intermediate and to a forwardmost position, and the activator link is vertically movable to a lowermost and to an uppermost position. An indexing and interrupter assembly is rotatably mounted on the forward end of the support member, said assembly comprising an indexing ratchet having a predetermined number of ratchet teeth and an interrupter disc having at least one disengager arm contact surface and at least one disengager arm receiving notch. An indexing pawl is pivotally mounted on the hammer, the pawl engaging the teeth of the indexing ratchet and rotating said indexing and interrupter assembly one tooth at a time each time a cartridge is fired. When the activator link is at its rearwardmost position, it is out of engagement with the forward end of the support member, thereby permitting the secondary sear to remain in engagement with the secondary sear notch of the hammer after each round is fired. When the activator link is at its intermediate position, the activator link engages the rearward end of a rocker arm and is also moved into position to contact the interrupter disc. When the bolt of the firearm is closed the rearward end of the rocker arm is at its upper position and the activator link is brought into contact with the interrupter disc. When the bolt is moved rearwardly to its open position, the rearward end of the rocker arm moves downwardly and the activator link is moved out of contact with the interrupter disc. When the upwardly moving activator link contacts an arm contact surface of the interrupter disc, the secondary sear is moved out of engagement with the secondary sear notch and the firearm fires automatically. When the activator link enters an arm receiving notch of the interrupter disc, the secondary sear remains in engagement with the secondary sear notch and automatic firing is interrupted. When the activator link is at its forwardmost position, it contacts the interrupter disc and moves the support arm upwardly each time a round is fired, thereby firing the firearm automatically as long as the trigger is pulled.

United States Patent [191 Ruger et al.

[111 3,847,054 1 1 Nov. 12, 1974 1 BURST FIRE MECHANISM FOR AUTO-LOADINGFIREARM [75] Inventors: William B. Ruger, Southport; Harry H. Sefried,II, New Haven, both of Conn.

[73] Assignee: Sturm, Ruger & Co. Inc., Southport,

Conn.

[22] Filed: Sept. 21, 1973 [21] Appl. No.: 396,662

Primary ExaminerStephen C. Bentley Attorney, Agent, or FirmPennie &Edmonds 7 1 ABSTRACT An auto-loading firearm that may be firedsemiautomatically and fully automatically is provided with a firingmechanism that permits bursts of, say, three rounds to be fired eachtime the trigger is pulled. The mechanism comprises a secondary seardisengager and interrupter support member pivotally mounted on the frameof the firearm so that upward movement of the forward end of the supportmember will cause the upper end of the secondary sear to move rearwardlyout of engagement with the secondary sear notch of the hammer. Anautomatic fire activator link is pivotally mounted on an activator linkpositioner which, in turn, is pivotally mounted on the frame. Theactivator link positioner and the activator link are longitudinallymovable to a rearwardmost, to an intermediate and to a forwardmostposition, and the activator link is vertically movable to a lowermostand to an uppermost position. An indexing and interrupter assembly isrotatably mounted on the forward end of the support mem her, saidassembly comprising an indexing ratchet having a predetermined number ofratchet teeth and an interrupter disc having at least one disengager armcontact surface and at least one disengager arm receiving notch. Anindexing pawl is pivotally mounted on the hammer, the pawl engaging theteeth of the in dexing ratchet and rotating said indexing andinterrupter assembly one tooth at a time each time a cartridge is fired.When the activator link is at its rearwardmost position, it is out ofengagement with the forward end of the support member, therebypermitting the secondary sear to remain in engagement with the secondarysear notch of the hammer after each round is fired. When the activatorlink is at its intermediate position, the activator link engages therearward end of a rocker arm and is also moved into position to contactthe interrupter disc. When the bolt of the firearm is closed therearward end of the rocker arm is at its upper position and theactivator link is I brought into contact with the interrupter disc. Whenthe bolt is moved rearwardly to its open position, the rearward end ofthe rocker arm moves downwardly and the activator link is moved out ofcontact with the interrupter disc. When the upwardly moving activatorlink contacts an arm contact surface of the interrupter disc, thesecondary sear is moved out of engagement with the secondary sear notchand the firearm fires automatically. When the activator link enters anarm receiving notch of the interrupter disc. the secondary sear remainsin engagement with the secondary sear notch and automatic firing isinterrupted. When the activator link is at its forwardmost position, itcontacts the interrupter disc and moves the support arm upwardly eachtime a round is fired, thereby firing the firearm automatically as longas the trigger is pulled.

10 Claims, 19 Drawing Figures PATENTEUHUV 12 new 3L847l054 SHEET 2 0F 8PATENTEBHUV 12 m: 3847 054 sum 3 or a PATENTEHHUY 12 1914 3.847054 SHEET5 BF 8 Wmmm 112 $74 3,847,054

SHEET 80F 8 BURST FIRE MECHANISM FOR AUTO-LOADING FIREARM BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates toautoloading firearms, and in particular to a firing mechanism for suchfirearms capable of firing a burst comprising a predetermined number ofrounds.

2. Prior Art Auto-loading firearms, for example, automatic rifles, arewell known in the art. Many such firearms, and in particular militaryarms, are designed to be fired both semi-automatically in which mode oneround is fired each time the trigger is pulled and fully automaticallyin which mode the firearm fires continuously as long as the trigger ispulled. When the firearm is in its fully automatic mode of operation, itis frequently desirable to fire relatively short bursts of, say, threeor four rounds per burst to conserve ammunition and to improve accuracy.Burst fire mechanisms for automatic firearms have heretofore beenproposed. However, these prior burst fire mechanisms are generallyoverly complicated and unreliable, and in any case these mechanisms aregenerally unadaptable for use with the type of automatic firearm withwhich the present invention is concerned.

After an intensive investigation of the problems inherent in the designand functioning of burst fire mechanisms for auto-loading firearms, wehave now devised an improved firing mechanism for such firearms which isversatile, reliable, and uncomplicated.

SUMMARY OF THE INVENTION The burst fire mechanism of the invention isapplicable to the general type of auto-loading firearms having a frame,a barrel secured to the frame, a bolt mounted for longitudinal travel inthe frame behind the barrel, and an auto-loading mechanism for movingthe bolt from its forward closed position to its rearward open positionand return when the firearm is fired. The autoloading mechanism may beof the gas operated, recoil operated, or blow-back type, providedrearward and forward movement of the bolt results directly or indirectlywith a rocking movement of a rocker arm pivotally mounted on the frame.The pivotally mounted hammer is formed with a primary sear notch andwith a secondary sear notch, and the pivotally mounted trigger isprovided with a primary sear for engaging the primary sear notch of thehammer. A secondary sear is pivotally mounted on the frame for engagingthe secondary sear notch of the hammer. The aforementioned rocker arm ispivotally mounted on the frame, the rearward end of rocker arm beingmoved upwardly when the bolt is at its forward closed position and beingmoved downwardly when the bolt is moved to its rearward open position.The upward and downward movement of the rocker arm alternately causesthe secondary sear to be disengaged from and permitting the secondarysear to engage the secondary sear notch of the hammer.

The improved firing mechanism of the invention is capable of firingsemi-automatically, fully automatically, and in bursts of predeterminedduration. The firing mechanism comprises a secondary sear disengager andinterrupter support member pivotally mounted on the frame. Upwardmovement of the forward end of the pivoted support member causes theupper end of the secondary sear to move rearwardly out of engagementwith the secondary sear notch of the hammer. An indexing and interrupterassembly is.rotatably mounted on the forward end of the support member,said assembly comprising an indexing ratchet having a predeterminednumber of ratchet teeth and an interrupter disc having at least onedisengager arm contact surface and at least one disengager arm receivingnotch. An indexing pawl is pivotally mounted on the hammer, said pawlengaging the teeth of said indexing ratchet and causing said indexingand interrupter assembly to rotate one tooth at a time each time acartridge is fired. An activator link positioner is pivotally mounted onthe frame for longitudinal movement to a rearwardmost to an intermediateand to a forwardmost position. An automatic fire activator link ispivotally mounted on the activator link positioner, said activator linkhaving rocker arm engaging means adapted to engage the rearward end ofthe rocker arm and a secondary sear disengager arm adapted to contactthe interrupter disc of the indexing and interrupter assembly, saidrocker arm engaging means and said secondary sear disengager arm beingmovable forwardly and rearwardly by corresponding movement of theactivator link positioner and being movable upwardly and downwardly whenin engagement therewith. The secondary sear disengager arm moves theforward end of the secondary sear and interrupter support memberupwardly to disengage the secondary sear when the disengager arm ismoved forwardly by the activator link positioner and is moved upwardlyby the rocker arm into contact with an arm contacting surface of theinterrupter disc.

When the activator link positioner is moved to its rearwardmostposition, the activator link is placed at its semiautomatic fireposition at which the rocker arm engaging stud is out of engagement withthe rearward end of the rocker arm and the disengager arm is out ofposition to contact the interrupter disc of the indexing and interrupterassembly.

When the activator link positioner is moved to its intermediateposition, the activator link is placed at its burst fire position atwhich the rocker arm engaging stud is in engagement with the rearwardend of the rocker arm and the forward end of the disengager arm is inposition to contact the .arm contact surfaces and to enter the armreceiving notches of the interrupter disc when the disengager arm iscaused to move upwardly by the rocker arm. When the activator linkpositioner is moved to its forwardmost position the activator link isplaced at its fully automatic fire position at which the rocker armengaging stud is in engagement with the rearward end of the rocker armand the forward end of the disengager arm is in position to contact thearm contact surfaces of the interrupter disc and is forward of theposition at which it can enter the arm receiving notches of theinterrupter disc when the disengager arm is caused to move upwardly bythe rocker arm.

In an advantageous embodiment of the invention a manually movable firingmode selector is pivotally mounted on the frame, the selector beingconnected to the activator link positioner and being adapted to move theactivator link positioner to its rearwardmost, its intermediate and itsforwardmost positions. Other advantageous features of the firingmechanism of the invention will be apparent from the following detaileddescription thereof.

BRIEF DESCRIPTION OF THE DRAWINGS The improved firing mechanism of theinvention will be better understood from the following descriptionthereof in conjunction with the accompanying drawings of which:

FIG. 1 is a fragmentary side elevation of an autoloading rifle embodyingthe invention.

FIG. 2 is a sectional view along an irregular vertical plane extendinglongitudinally through the receiver portion and the adjacent stock andforearm portions of the rifle of FIG. 1.

FIG. 3 is a fragmentary perspective view of the receiver showing thefire control selector and the rocker arm pivotally mounted thereon.

FIG. 3a is an exploded view of the fire control selector assembly.

FIG. 4 is a perspective view of the trigger housing assembly.

FIG. 5 is a perspective view of the rearward end of the receiver showingwhere the selector assembly is pivotally mounted thereon.

FIG. 6 is an exploded view of the trigger housing assembly of FIG. 4.

FIG. 7 is a sectional view along line 7-7 of FIG. 8

showing the fire control selector assembly as it is mounted on thereceiver.

FIG. 8 is a fragmentary view of the firing mechanism, with parts brokenaway for better visibility, showing the firing mechanism in its burstfire mode at the start of the burst firing cycle with the trigger atrest and the hammer cocked and ready for firing.

FIG. 9 is a fragmentary view similar to FIG. 8 showing the firingmechanism in its burst fire mode in the middle of the burst firing cyclewith the trigger pulled, the bolt open, and the hammer held temporarilyby the secondary sear.

FIG. 10 is a fragmentary sectional view through the trigger andsecondary sear showing the indexing ratchet and pawl mechanism and theindexing detent arrangement.

FIG. 11 is a fragmentary view similar to the left hand portion of FIG. 9showing the firing mechanism in its burst fire mode in the middle of theburst firing cycle with the trigger pulled, the bolt closed, and thesecondary sear moved rearwardly out of engagement with the secondarysear notch thereby releasing the hammer.

FIG. 12 is a fragmentary view similar to FIG. 11 showing the firingmechanism in its burst fire mode at the end of the burst firing cyclewith the trigger pulled, the bolt closed, the disengager arm received inthe disengager arm receiving notch of the interrupter disc, and thehammer held in its rearward position by the secondary sear.

FIG. 13 is a perspective view of the secondary sear, the interrupter andindexing ratchet assembly and the indexing pawl showing the relativepositions of these parts.

FIG. 14 is a fragmentary view of the firing mechanism, with parts brokenaway for better visibility, showing the firing mechanism in its fullyautomatic mode in the middle of the automatic firing cycle with thetrigger pulled, the bolt open, and the hammer held temporarily by thesecondary sear.

FIG. 15 is a fragmentary view similar to FIG. 14 showing the firingmechanism in its fully automatic mode with the trigger pulled, the boltclosed, and the secondary sear withdrawn from engagement with thesecondary sear notch, thereby releasing the hammer.

FIG. 16 is a fragmentary view of a modification of the secondary scarand interrupter support arm arrangement with portions of the trigger insection.

FIG. 17 is a perspective view of the modified secondary sear andinterrupter support arm arrangement shown in FIG. 16.

FIG. 18 is an exploded view of the trigger and the secondary sear andinterrupter support arm assembly shown in FIG. 17.

DETAILED DESCRIPTION As shown best in FIG. 1, the principal externallyvisible components of a typical gas-operated auto-loading rifle of thetype to which the present invention relates include a barrel 10, areceiver 11 to which the barrel is secured, a longitudinally movablebolt 12 mounted in the receiver 11 behind the barrel 10, alongitudinally movable slide 13 having a slide cocking handle 14 that isconnected to the bolt 12, a trigger l5 and trigger guard 16, a magazine17 and magazine latch 18, a stock 19 having a stock forearm 20, aforearm upperhand guard 21, a gas block 22 having a block clamp portion23, a rear sight 24, and a safety activating lever 25. As shown in FIG.2, the stock 19 is formed with a vertical slot or cut-out portion 26 inwhich the magazine 17 and the firing mechanism associated with thetrigger 15 are received, and the stock forearm 20 is formed with achannel-shaped recess 27 in which the forward end of the slide 13 andthe parts associated therewith are received.

Referring again to FIG. 2, the barrel 10 is formed with a bore 28 havinga cartridge chamber 29 at the rearward end thereof. The longitudinallymovable bolt 12 is provided with a firing pin 30 in position to strike acartridge received in the chamber 29, an extractor (not shown) and aspring loaded ejector 32. The trigger 15 is pivotally mounted on thetrigger housing 34 by means of the trigger pivot pin 35 that extendsthrough the pivot hole 36 (shown best in FIG. 6) formed in the trigger15. The trigger 15 is provided with a positioner pivot receiving slot37, with a sear arm and primary sear 38 and with a trigger spring 39.Secondary sear 40 is also mounted on the pivot pin 35, the secondarysear being provided with a secondary sear spring 41. A hammer 42 ispivotally mounted on the housing 34 by means of the hammer pivot pin 43in position to strike the rearward end of the firing pin 30 when thebolt 12 is in its closed position. The hammer 40 is provided with arearwardly extending sear notch arm having a primary sear notch 45 and asecondary sear notch 46. A hammer strut 47 and spring 48 presses thehammer 42 toward its firing position as shown in FIG. 2. The receiver l1and the parts associated therewith is inserted into the slot 26 fromabove and the trigger housing 34 and the parts associated therewith isinserted into the slot 26 from below, the receiver 11 and the housing 34being secured together to form an assembly referred to herein and in theclaims as the frame.

The magazine 17 is adapted to contain a plurality of cartridges 50 andis located in the slot 26 of the stock 19 directly below the bolt 12when the bolt is in its closed position. The magazine 17 advantageouslycomprises a box-like structure that is removable from the slot 25, themagazine being held in position in the slot by the front magazine latch51 and the manually operated r'ear magazine latch 18. A magazinefollower 52 is disposed within the magazine 17 below the cartridge 50,the magazine follower having a follower spring (not shown) that pressesthe magazine follower upwardly, thereby moving the cartridge 50 intoposition to be loaded into the chamber 29 by the bolt 12.

As noted, the auto-loading mechanism is preferably gas operated,although other types of mechanisms (for example recoil and blow-backmechanisms) are well known in the art, the action shown in the drawingsbeing a modification of the bolt and auto-loading mechanism of the M-l4rifle. In this modification a slide block (not shown) is located withinthe channelshaped recess 27 of the forearm 20, the slide block beingconnected to the slide 13 and being held in its forward position by theslide spring 54 that is mounted on the slide spring guide rod 55. Whenthe rifle is fired, powder combustion gases drive the slide blockrearwardly against the pressure of the slide spring 54 thereby causingthe bolt 12 to move rearwardly to its open position, the slide spring 54then moving the bolt 12 forwardly to its closed position in a mannerwell known in the art.

The rifle may be fired in any of three distinct modes of operationnamely, a semi-automatic mode in which one round is fired each time thetrigger is pulled; a burst fire mode in which a burst of, say, threerounds is fired each time the trigger is pulled; and a fully automaticmode in which the rifle fires continuously as long as the trigger ispulled. A fire control selector 57 is pivotally mounted on the side ofthe receiver 11. When the selector 57 is at the position S shown inFIGS. 1, 2 and 3 the firing mechanism is placed in its semiautomaticmode of operation, when the selector 57 is at the position B shown inFIGS. 8, 9 and 12 the firing mechanism is placed in its burst fire modeof operation, and when the selector 57 is at the position A shown inFIGS. 14 and 15 the firing mechanism is placed in its fully automaticmode of operation.

In all modes of operation the firing mechanism is in its cocked andready-to-fire condition when the hammer 42 is rotated rearwardly againstthe pressure of the hammer strut 47 and spring 48 so that the primarysear notch 45 is engaged and held by the primary sear 38, when a livecartridge is in the chamber 29 and when the bolt 12 is in its closed andlocked position. When the firing mechanism is in its semi-automatic modeof operation, the trigger 15 is pulled to disengage the primary sear 38from the primary sear notch 45, thereby allowing the hammer 42 to springforward against the rearward end of the firing pin 30 which, in turn,strikes and fires the cartridge in the chamber 29. Powder combustiongases force the slide 13 and the bolt 12 rearwardly against the pressureof the slide spring 54. Rearward movement of the bolt 12 rotates thehammer 42 rearwardly so that the secondary sear notch 46 of the hammeris engaged and held by the secondary sear 40. The pressure of the slidespring 54 then causes the slide 13 and the bolt 12 to move forwardly totheir closed positions. When the trigger 15 is released and allowed toreturn to its usual position, the primary sear notch 45 is engaged andheld by the primary sear 38 while, at the same time, the secondary searnotch 46 is released by the secondary sear 40. The rifle is now again inits cocked and ready-to-fire position. This sequence of operations maybe repeated one shot at a time until the magazine 17 is empty.

When the firing mechanism is in its burst fire mode of operation and isin its ready-to-fire condition, pulling the trigger 15 disengages theprimary sear-38 from the primary sear notch 45 thereby releasing thehammer 42 and firing the cartridge in the chamber 29. Powder combustiongases force the slide 13 and the bolt 12 rearwardly against the pressureof the slide spring 54, and rearward movement of the bolt 12 rotates thehammer 42 rearwardly so that the secondary sear notch 46 of the hammeris engaged and held temporarily by the secondary sear 40. The pressureof the slide spring 54 then causes the slide 13 and the bolt 12 to moveforwardly to the bolt closed position. As soon as the bolt 12 is closedand locked the automatic fire mechanism causes the secondary sear 40 tobe disengaged from the secondary sear notch 46 thereby allowing thehammer 42 to spring forwardly and fire the fresh cartridge in thechamber 29 as in fully automatic operation. This sequence of operationsis repeated automatically until a predetermined number of rounds ofammunition (say, three rounds) have been fired. When the predeterminednumber of rounds have been fired an automatic fire interrupter mechanismcauses the secondary sear 40 to remain in engagement with the secondarysear notch 46 and to hold the hammer 42 in its cocked position after thebolt 12 is closed and locked. When the trigger is released and allowedto return to it usual position, the primary sear notch 45 of the hammeris en gaged and held by the primary sear 38 while, at the same time, thesecondary sear notch 46 is released by the secondary sear 40. Once againthe rifle is in its cocked and ready-to-fire condition.

When the firing mechanism is in its fully automatic mode of operationand is in its ready-to-fire condition, pulling the trigger 15 disengagesthe primary sear 38 from the primary sear notch 45 which allows thehammer 42 to spring forward and fire the cartridge in the chamber 29.Rearward travel of the slide 13 and the bolt 12 rotates the hammer 42rearwardly so that the secondary sear notch 46 is engaged and heldtemporarily by the secondary sear 40. When the bolt 12 moves forwardlyto its closed and locked position the automatic fire mechanismdisengages the secondary sear 40 from the secondary sear notch 46thereby allowing the hammer 42 to spring forwardly and fire the freshcartridge in the chamber 29. This sequence of operations is repeateduntil the trigger 15 released and allowed to return to its usualposition at which position the primary sear notch 45 of the hammer 42 isengaged and held by the primary sear 38 of the trigger. As before, therifle is again in its cocked and ready-to-fire condition.

As shown best in FIGS. 3 and 3a, the fire control selector assembly 57comprises a selector thumb piece 58, a selector arm 59, a retaining pin60, and a retaining pin detent spring 61 and plunger 62. The selectorthumb piece is formed with a selector shaft receiving hole 63, aretaining pin groove 64, and a detent spring and plunger receiving hole65. The selector arm 59 is provided wiJh a selector shaft 66 and with apositioner engaging stud 67, the shaft 66 being formed with a retainingpin receiving hole 68. The fire control selector assembly is mounted onthe receiver 11 by inserting the shaft 66-into the shaft pivot hole 70formed in the receiver (FIG. The thumb piece 58 is then mounted on theshaft and the retaining pin 60 is inserted in the groove 64 and throughthe hole 68, the retaining pin 60 7 being held in place by the detentspring 61 and plunger 62 which have previously been inserted in the hole65. When mounted on the receiver as shown in FIG. 3 the selectorassembly 59 can be rotated to any one of the three positions marked S,B, or A (shown best in FIG. 5 of the drawing), the selector beingdetained in the selected position by the detent lug 71 on the inwardfacing surface of the thumb piece 58 which is releasably received in oneof the detent recesses 72 formed in the receiver 11, as shown best inFIG. 7.

As shown best in FIGS. 2, 4, 6, and 8, an activator link positioner 73is pivotally mounted on the trigger housing 34 by means of thepositioner pivot stud 74. The positioner pivot stud 74 extends throughthe positioner pivot receiving slot 37 formed in the trigger l5 andserves as the backstop for the trigger spring 39. The activator linkpositioner 73 is provided with an activator pivot stud 75 on which theautomatic fire activator link 76 is pivotally mounted and with apositioner engaging stud receiving slot 77 in which the positionerengaging stud 67 of the fire control selector 57 is received. Theautomatic fire activator link 76 is provided with a pivot hole 78 inwhich the activator pivot stud 75 is received, a rocker arm engagingstud 79, a secondary sear disengager arm 80, and a trigger pivot pinreceiving slot 81. The activator link is also formed with preventer lugengaging surfaces 82, 83 and 84 as hereinafter described. A retainingring 85 retains the activator pivot stud 75 in the pivot hole 78.

As shown best in FIGS. 3, 8 and 9, a longitudinally extending rocker arm87 is pivotally mounted on the member 88 that depends from the righthand side of the receiver 11. The forward end of the rocker arm 87 isprovided with a slide contacting finger 89 that extends upwardly throughan opening 90 formed in the receiver 11 beneath the slide handle 14 ofthe slide 13, and the rearward end of the rocker arm 87 is provided witha fork-like member that is formed with a stud receiving slot 92 that isadapted to receive the rocker arm engaging stud 79 of the automatic fireactivator link 76. A rocker arm spring 93 urges the rearward end of thepivoted rocker arm 87 downwardly and the forward end upwardly. The slidehandle 14 is provided with a rocker arm depressor lug 94 which contactsthe slide contacting finger 89 of the rocker arm 87 when the slidehandle 14 is at its forwardmost position, the depressor lug 94 forcingthe forward end of the rocker arm downwardly and the rearward endupwardly against the pressure of the spring 93 as shown in FIG. 8. Whenthe slide handle 14 is moved rearwardly the rocker arm depressor lug 94is moved out of contact with the slide contacting finger 89 of therocker arm 87 thereby allowing the forward end of the rocker arm to moveupwardly and the rearward end of the rocker arm to move downwardly asshown in FIG. 9.

It will be understood that other types of rocker arm engaging means maybe substituted for the rocker arm engaging stud 79 of the activator link76 and the stud receiving slot 92 of the rocker arm 87. For example, thepositions of the stud 79 and slot 92 may be exchanged, or an idler linkarrangement may be employed. Other equivalent rocker arm engaging meanswill be apparent to those skilled in the art.

As shown best in FIG. 2, when the tire control selector 5 is at itssemi-automatic fire position S, the activator link positioner 73 isrotated about the pivot stud 74 to its rearwardmost position, and theautomatic fire activator link 76 is moved to its rearwardmost positionat which position the trigger pivot pin 35 is received in the pinreceiving slot 81 of the activator link and the rocker arm engaging stud79 is out of engagement with the stud receiving slot 92 of the rockerarm 87. As shown best in FIGS. 8 and 9, when the fire control selector57 is at its burst fire position B, the activator link positioner 73 isrotated about the pivot stud 74 to a position intermediate itsrearwardmost (FIG. 2) and its forwardmost (FIG. 14) positions, and theautomatic fire activator link 76 is moved to its intermediate positionat which position the trigger pivot pin 35 is moved out of engagementwith the pin receiving slot 81 and the rocker arm engaging stud 79 ismoved into engagement with the stud receiving slot 92 of the rocker arm87. As shown best in FIGS. 14 and 15, when the fire control selector 57is at its fully automatic fire position A the activator link positioner73 is rotated about the pivot stud 74 to its forwardmost position, andthe automatic fire activator link 76 is moved to its forwardmostposition at which position the rocker arm engaging stud 79 is receivedin the stud receiving slot 92 of the rocker arm 87.

As shown in FIGS. 8 and 9 and in FIGS. 14 and 15, when the rocker armengaging stud 79 of the automatic activator link 76 is received in thestud receiving slot 92 of the rocker arm 87, the activator link 76 iscaused to move upwardly and then downwardly about the pivot-stud whenthe rearward end of the rocker arm 87 is moved upwardly by the rockerarm depressor lug 94 and then downwardly by the rocker arm spring 93, ashereinbefore described. Upward and downward movement of the automaticfire activator link 76 about the pivot stud 75 causes the secondary seardisengager arm of the activator link 76 to move upwardly and downwardlyas hereinafter described.

A sear disengager and interrupter support member 96 is pivotally mountedon the trigger pivot pin 35. In the embodiment shown in FIGS. 2, 6 and 8through 15 of the drawings, the support member 96 is an integrallyformed part of the secondary sear 40 which, of course, is pivotallymounted on the pivot pin 35. In this embodiment the secondary searspring 41 urges the secondary sear 40 forwardly into engagement with thesecondary sear notch 46 of the hammer 42 and also urges the forward endof the integral support member 96 downwardly about the pivot pin 35. Inthe embodiment shown in FIGS. l6, l7 and 18 of the drawings, the supportmember 960 and the secondary sear 40a are separate parts both of whichare pivotally mounted on the pivot pin 35. In this embodiment thesecondary sear spring 41a urges the secondary sear 40a forwardly intoengagement with the secondary sear notch 46 of the hammer 42 and aseparate support member spring 97 urges the forward end of the separatesupport member 96a downwardly about the pivot pin 35.

In both embodiments, upward movement of the support member 96 or 960causes the secondary sear 40 or 40a to move rearwardly against thepressure of the secondary sear spring 41 or 410, respectively, and outof engagement with the secondary sear notch 46 of the hammer 42. In thefirst embodiment, the support member 96 is an integrally formed part ofthe secondary sear 40. In the second embodiment, the support member 96ais provided with a secondary sear stop surface 98 that is contacted bythe laterally extending stop engaging lug 99 of the secondary sear 40aso that, when the support member 96a is moved upwardly about the pivotpin 35, the secondary sear 40a is moved rearwardly about the pivot pin35. Conversely, forward movement of the secondary sear 40 or 40a beyonda predetermined point is prevented by blocking downward movement of theintegral support member 96 or the separate support member 96a by meansof the support member lifting lug 100 of the trigger 15. The supportmembers 96 and 96a are caused to move upwardly, and thereby to disengagethe secondary sear 40 or 40a, by the support member lifting lug 100 ofthe trigger or by the secondary sear disengager arm 80 of the activatorlink 76, as hereinafter described.

A burst fire indexing and interrupter assembly is rotatably mounted onthe forward end of the interrupter support members 96 and 96a. As shownbest in FIGS. 6, 10, 13 and 18, the indexing and interrupter assemblycomprises an interrupter shaft 102 having an interrupter disc 103secured to one end thereof and having an indexing ratchet 104 mounted onthe ratchet stud 105 at the opposite end thereof and secured thereto bythe ratchet pin 106. The interrupter shaft 102 is rotatably mounted inthe shaft receiving hole 107 formed in the forward end of the supportmember 96 (and support member 96a). The indexing ratchet 104 is formedwith a predetermined number (for example, six) of ratchet teeth 108, andthe interrupter shaft 102 is formed with a corresponding number ofinterrupter detent recesses 109. A detent plunger 110 and spring 111 isreceived in the plunger receiving hole 112 formed in the support member96, the spring pressed plunger 110 engaging one of the detent recesses109 in the interrupter shaft 102 to releasably detain the indexingratchet 104 and interrupter disc 103 at a given index position.

The outer periphery of the interrupter disc 103 is provided withsecondary sear disengager arm contact surfaces 114 and with secondarysear disengager arm receiving notches 115. When the interrupter disc 103is rotated to a position at which the disengager arm contact surface 114is directly above the end of the disengager arm 80 as shown in FIGS. 9and 11, and when the disengager arm 80 is moved upwardly by the actionof the rocker arm 87 as shown in FIG. 11, the disengager arm 80 willcontact the arm contact surface 114 and move the end of support member96 upwardly about the pivot pin 35. As previously noted, when thesecondary sear notch 46 is engaged by the secondary sear 40 (or 40a)upward movement of the support member 96 (and 96a) moves the secondarysear 40 (and 40a) rearwardly about the pivot pin 35 and out ofengagement with the secondary sear notch 46 of the hammer 42. When theinterrupter disc 103 is rotated to a position at which one of the armreceiving notches 115 is directly above the end of the disengager arm 80as shown in FIG. 12, upward movement of the disengager arm 80 caused bythe action of the rocker arm 87 will move the end of the disengager arminto the arm receiving notch 115 and thereby avoid upward move ment ofthe forward end of the support member 96 with concomittant disengagementof the secondary sear 40.

An indexing pawl 117 having a ratchet engaging pawl,

tooth 118 is pivotally mounted on the hammer 42 by means of the pawlpivot pin 119 in position to engage the ratchet teeth 108 of theindexing ratchet 104. As shown best in FIGS. 6 and 10, a pawl supportpin 120 on the inner surface of the safety 25 supports the pawl 117 andmaintains the pawl tooth 118 in position to engage the ratchet teeth 108of the indexing ratchet 104. In addition, a pawl spring 121 may beprovided which urges the pawl 117 upwardly against the indexing ratchet104 and thereby helps maintain the pawl tooth 118 in engagement with theratchet teeth.

When thehammer 42 is in its forward position as shown in FIGS. 2 and 4and in outline in FIG. 10, the pawl tooth 118 of the indexing pawl 117is outof engagement with the ratchet teeth 108 of the indexing ratchet104. As shown best in FIG. 10, when the rifle is fired (or manuallycocked), the hammer 42 rotates rearwardly to its cocked position therebycausing the pawl tooth 118 to engage one of the teeth 108 of theindexing ratchet 104 and to rotate the indexing ratchet a predeterminedfractional part of a complete revolution (in the present case, one-sixthof a complete revolution). The spring loaded detent plunger engages thecorresponding detent recess 109 to prevent further rotation of theindexing ratchet 104. Thus, it will be seen that each time the rifle isfired the indexing pivot 117 will cause the indexing ratchet 104 and theinterrupter disc 103 to rotate an angular distance equivalent to theangular spacing of the ratchet teeth 108, one tooth at a time. That isto say, when the riflev is in its semi-automatic mode of operation theindexing ratchet 104 and the interrupter disc 103 will be rotated anangular distance equivalent to the angular distance between the teeth108 of the ratchet 104 each time the trigger 15 is pulled. When therifle is in its burst fire mode of operation the indexing ratchet 104and interrupter disc 103 will be rotated on an angular distancecorresponding to the number of rounds fired in each burst. When therifle is in its fully automatic mode of operation, the rifle will firecontinuously as long as the trigger 15 is pulled and the indexingratchet 104 and interrupter disc 103 will be rotated an angular distancecorresponding to the number of rounds that are fired.

When the rifle is in its burst fire mode of operation, the number ofrounds fired in each burst (that is, each time the trigger is pulled) isdetermined by the number of ratchet teeth 108 on the indexing ratchet104 and by the number of disengager arm receiving notches formed in theinterrupter disc 103. Automatic fire is interrupted when the interrupterdisc 103 is rotated to the position at which the disengager arm 80 willenter an arm receiving notch 115 formed in the interrupter disc. In theembodiment shown in the drawings, the indexing ratchet 104 is formedwith six ratchet teeth I08 and the interrupter disc 103 is formed withtwo disengager arm receiving notches 115. As a consequence, every timethe rifle fires one round the indexing ratchet 104 and the interrupterdisc 103 will be rotated onesixth of a revolution, and after threerounds the interrupter disc will have been rotated one-half a revolutionto bring one of the arm receiving notches 115 into posi-.

tion to receive the end of the disengaging arm 80 and thereby interruptthe automatic firing of'the rifle. The system permits great versatilityin the length of the burst fire sequence. For example, the combinationof an indexing ratchet 104 having six ratchet teeth 108 with aninterrupter disc 103 having three equally spaced arm receiving notchs115 would provide a burst of two rounds each time the trigger is pulled;the combination of an indexing ratchet having eight ratchet teeth 108with an interrupter disc having two arm re ceiving notches 115 wouldprovide a burst of four rounds; the combination of an indexing ratchethaving five ratchet teeth 108 with an interrupter disc having one armreceiving notch 115 would provide a burst of five rounds; and so on upto the limit imposed by the physical dimensions of the parts involved.Moreover, the burst fire mode of operation can be eliminated byproviding an interrupter disc 103 having no arm receiving notches, andthe fully automatic mode of operation can be eliminated by blockingmovement of the fire control selector 57 or the activator linkpositioner 73 or the automatic fire activator link 76 into theirrespective automatic fire positions.

As previously noted, the firing mechanism is in its cocked andready-to-fire condition when the hammer is rotated rearwardly againstthe pressure of the spring loaded hammer strut 47 so that the primarysear notch 45 is engaged and held by the primary sear 38, when a livecartridge is in the chamber 29, and when the bolt 12 is in its closedand locked position. This ready-tofire condition of the rifle is shownbest in FIG. 8 in connection with the burst fire mode of operation.

When the fire control selector knob 57 is rotated to the position S asshown in FIGS. 1, 2 and 3, the firing mechanism is placed in itssemi-automatic mode of operation. In its semi-automatic mode, theactivator link positioner 73 is at its rearwardmost position, and theautomatic fire activator link 76 is also at its rearwardmost position atwhich position the trigger pivot pin 35 is received in the pin receivingslot 81 of the activator link and the rocker arm engaging stud 79 is outof engagement with the stud receiving slot 92 of the rocker arm 87. Whenthe firing mechanism is in its ready-tofire condition, the trigger 15 ispulled to disengage the primary sear 38 from the primary sear notch 45thereby allowing the hammer 42 to spring forward against the rearwardend of the firing pin 30 which, in turn, strikes and fires the cartridgein the chamber 29. Pulling the trigger l5 rearwardly about the pivot pin35 moves the support member lifting lug 100 downwardly a correspondingdistance, thereby allowing the support member 96 (or 96a) to movedownwardly and the secondary sear 40 (or 40a) to move forwardly intoposition to engage the secondary sear notch 46 of the hammer 42. Inaddition, rearward movement of the trigger moves the activator movementpreventer lug 123 into engagement with the preventer receiving surface82 thereby preventing movement of the activator link positioner 73 whenthe rifle is fired.

When the cartridge is fired, powder combustion gases force the slide 13,the slide handle 14 and the bolt 12 from their forward closed positionsto their rearward positions. Rearward movement of the slide handle 14allows the forward end of the rocker arm 87 to move upwardly whichcauses the rearward end of the rocker arm to move downwardly from itsupper position to its lower position as previously described. However,as the rocker arm engaging stud 79 of the activator link 76 is out ofengagement with the stud receiving slot 92 of the rocker arm 87, thedownward movement of the rearward end of the rocker arm has no effect onthe firing sequence. Rearward movement of the bolt 12 extracts andejects the spent cartridge case and also rotates the hammer 42rearwardly so that the secondary sear notch 46 of the hammer is engagedand held by the secondary sear 40 (or 40a).

The pressure of the slide spring 54 then causes the slide 13 to moveforwardly carrying with it the slide handle 14 and the bolt 12. As thebolt 12 moves from its open position to its closed position, it picks upa fresh cartridge 50 from the magazine 17 and inserts the cartridge inthe chamber 29 in the manner known in the art. When the slide handle 14reaches its forward closed position, the depressor lug 94 forces theforward end of the rocker arm 87 downwardly which moves the rearward endof the rocker arm upwardly as previously described. However, as therocker arm engaging stud 79 is out of engagement with the stud receivingslot 92, upward movement of the rearward end of the rocker arm 87 has noeffect on the firing sequence. When the trigger 15 is released andallowed to return to its usual position, the primary sear notch 45 ofthe hammer is engaged and held by the primary sear 38 of the triggerwhile, at the same time, the secondary sear notch 46 is released by thesecondary sear 40 (or 40a That is to say, forward movement of thetrigger 15 to its usual position causes the support member lifting lug100 to move upwardly a corresponding distance thereby moving the supportmember 96 (or 96a) upwardly and the secondary sear 40 (or 40a rearwardlyout of engagement with the secondary sear notch 46. The rifle is nowonce again in its cocked and ready-to-fire position. This sequence ofoperations may be repeated one shot at a time until the magazine 17 isempty.

When the fire control selector knob 57 is rotated to the position B asshown in FIGS. 8, 9, 11 and 12, the firing mechanism is placed in itsburst fire mode of operation. In its burst fire mode, the activator linkpositioner 73 and the automatic fire activator link 76 are at theirintermediate position at which position the trigger pivot pin 35 ismoved out of engagement with the pin receiving slot 81 of the actigatorlink and the rocker arm engaging stud 79 is moved into engagement withthe stud receiving slot 92 of the rocker arm 87, as shown best in FIG.8. In addition, the secondary sear disengager arm is moved forwardlyinto position to be received in the arm receiving notch 115 of theinterrupter disc 103 as shown in FIGS. 8 and 12 and to contact the armcontact surface 114 of the interrupter disc 103 as shown in FIGS. 9 and11.

When the firing mechanism is in its ready-to-fire condition as shown inFIG. 8, the trigger 15 is pulled to disengage the primary sear notch 45thereby allowing the hammer 42 to spring forward against the rearwardend of the firing pin 30 which, in turn, strikes and fires the cartridgein the chamber 29. Pulling the trigger 15 rearwardly about the pivot pin35 moves the support member lifting lug downwardly a corresponding distance, thereby allowing the support member 96 to move downwardly and thesecondary sear 40 to move forwardly into position to engage thesecondary sear notch 46 of the hammer 42. In addition, rearward movementof the trigger 15 moves the activator movement preventer lug 123 intoengagement with the preventer receiving surface 83 as shown in FIG. 9.

Powder combustion gases force the slide 13, the slide handle 14 and thebolt 12 rearwardly against the pressure of the slide spring 54. As shownin FIG. 9, reararm 87, the downward movement of the rearward end of therocker arm causes the activator link 76 to be rotated downwardly aboutthe pivot stud 75 which, in turn, moves the secondary sear disengagerarm 80 downwardly out of contact with the interrupter disc 103. Rearwardmovement of the bolt 12 rotates the hammer 42 rearwardly about the pivotpin 43 so that the secondary sear notch 46 of the hammer is engaged andtemporarily held by the secondary sear 40, as shown in FIG. 9. At thesame time, as shown best in FIG. 10, the tooth 118 of the indexing pawl117 engages one of the ratchet teeth 108 of the indexing ratchet 104thereby causing the indexing ratchet 104 and the interrupter disc 103 torotate an angular distance equivalent to the spacing of the ratchetteeth 108. This rotation moves the interrupter disc 103 from theposition shown in FIG. 8 to the position shown in FIG. 9 at which thearm contact surface 114 of the interrupter disc is in position to becontacted by the disengager arm 80 of the activator link 76.

The pressure of the slide spring 54 causes the slide 13 to moveforwardly carrying with it the slide handle 14 and the bolt 12. When theslide handle 14 reaches its forward closed position, the depressor lug94 forces the forward end of the rocker arm 87 downwardly which movesthe rearward end of the rocker arm upwardly, as previously described. Asshown best in FIG. 11, upward movement of the rearward end of the rockerarm 87 moves the activator link 76 upwardly about the pivot stud 75which, in turn, causes the secondary sear disengager arm 80 to contactthe arm contact surface 114 of the interrupter disc 103 and to move theforward end of the interrupter support member 96 upwardly about thetrigger pin 35. In the embodiment shown in FIGS. 8 to 13, the supportmember 96 is an integral part of the secondary sear 40 so that upwardmovement of the support member 96 causes the secondary sear 40 to moverearwardly out of engagement with the secondary sear notch 46 of thehammer 42. In the embodiment shown in FIGS. 16 to 18, the support member96a and the secondary sear 40a are separate parts both pivoted on thepivot pin 35. Upward movement of the support member 96a moves thesecondary sear 40a rearwardly out of engagement with the secondary searnotch 46 as previously described. When the secondary sear notch 46 isdisengaged as shown in FIG. 11, the hammer 42 is released and strikesthe firing pin 30 which, in turn, strikes and fires the cartridge in thechamber 29.

When the cartridge is fired, the slide 13, slide handle 14 and bolt 12move rearwardly and then forwardly to repeat the sequence of operationsdescribed in the preceding two paragraphs. The rifle is now firingautomatically. After three rounds are fired, the interrupter disc 103 isrotated to the position shown in FIG. 12 at which position thedisengager arm 80 is received in the arm receiving notch 115 of theinterrupter disc. As a result, upward movement of the rearward end ofthe rocker arm 87 with concomitant upward movement of the disengager arm80 does not move the forward end of the support member 96 (or 96a)upwardly and does not disengage the secondary sear 40 (or 40a) and thesecondary sear notch 46. Automatic firing of the rifle thereupon isinterrupted or stopped.- When the trigger 15 is released and allowed toreturn to its usual position, the primary sear notch 45 of the hammer isengaged and held by the primary sear 28 of the trigger while, at thesame time, the secondary sear notch 46 is released by the secondary sear40 (or 40a) in the manner previously described. The rifle is once againin its cooked and ready to fire condition as shown in FIG. 8.

When the fire control selector knob 57 is rotated to the position A" asshown in FIGS. 14 and 15, the firing mechanism is placed in itsautomatic mode of operation. In its automatic mode, the activator linkpositioner 73 and the automatic fire activator link 76 are at theirforwardmost position at which position the trigger pivot pin 35 is outof engagement with the pin receiving slot 81 of the activator link andthe rocker arm engaging stud 79 is in engagement with the stud receivingslot 92 of the rocker arm 87. In addition, as shown in FIGS. 14 and 15,the secondary sear disengager arm 80 is moved forwardly beyond the pointat which it can be received in the arm receiving notch 115 of theinterrupter disc 103, the disengager arm 80 being in position to contactthe arm contact surface 114 of the interrupter disc 103 as also shown inFIGS. 14 and 15.

When the firing mechanism is in its ready-to-fire condition(corresponding to the condition shown in FIG. 8), the trigger 15 ispulled to disengage the primary sear 38 from the primary sear notch 45thereby allowing the hammer 42 to spring forward against the rearwardend of the firing pin 30 which, in turn, strikes and fires the cartridgein the chamber 29. Pulling the trigger l5 rearwardly about the pivot pin35 moves the support member lifting lug 100 downwardly a correspondingdistance, thereby allowing the support member 96 to move downwardly andthe secondary sear 40 to move forwardly into position to engage thesecondary sear notch 46 of the hammer 42. In addition, rearward movementof the trigger 15 moves the activator movement preventer lug 123 intoengagement with the preventer receiving surface 84 as shown in FIG. 14.

Powder combustion gases force the slide 13, the slide handle 14 and thebolt 12 rearwardly against the pressure of the slide spring 54. As shownin FIG. 14, rearward movement of the slide handle 14 allows the forwardend of the rocker arm 87 to move upwardly which causes the rearward endof the rocker arm to move downwardly to the lower position. Because therocker arm engaging stud 79 of the activator link 76 is in engagementwith the stud receiving slot 92 of the rocker arm 87, the downwardmovement of the rearward end of the rocker arm causes the activator link76 to be rotated downwardly about the pivot stud which, in turn, movesthe secondary sear disengager arm downwardly out of contact with theinterrupter disc 103 as shown in FIG. 14. Rearward movement of the bolt12 rotates the hammer 42 rearwardly about the pivot pin 43 so that thesecondary sear notch 46 of the hammer is engaged and temporarily held bythe secondary sear 40, as shown in FIG. 14. At the same time, the tooth118 of the indexing pawl 117 engages one of the ratchet teeth 108 of theindexing ratchet I04 thereby causing the indexing ratchet I04 and theinterrupter disc 103 to rotate an angular distance equivalent to thespacing of the ratchet teeth 108. However, this rotation of theinterrupter disc 103 has no effect on the firing sequence as thesecondary sear disengager arm 80 has been moved forwardly beyond thepoint at which it can enter the arm receiving notches 115 formed in theinterrupter disc 103.

The pressure of the slide spring 54 causes the slide 13 to moveforwardly carrying with it the slide handle 14 and the bolt 12. When theslide handle 14 reaches its forward closed position, the depressor lug94 forces the forward end of the rocker arm 87 downwardly which movesthe rearward end of the rocker arm upwardly, as previously described. Asshown best in FIG. 15, upward movement of the rearward end of the rockerarm 87 moves the activator link 76 upwardly about the pivot stud 75which, in turn, causes the secondary sear disengager arm 80 to contactthe arm contact surface 114 of the interrupter disc 103 and to move theforward end of the interrupter support member 96 upwardly about thetrigger pin 35. In the embodiment shown in FIGS. 14 and 15, the supportmember 96 is an integral part of the secondary sear 40 so that upwardmovement of the support member 96 causes the secondary sear 40 to moverearwardly out of engagement with the secondary sear notch 46 of thehammer 42. In the embodiment shown in FIGS. 16 to 18, support member 96aand the secondary sear 40a are separate parts both pivoted on the pivotpin 35. Upward movement of the support member 96a causes the secondarysear stop surface 98 to contact the stop engaging lug 99 of thesecondary sear 40a and to move the secondary sear rearwardly out ofengagement with the secondary sear notch of the hammer 42. When thesecondary sear notch 46 is disengaged as shown in FIG. 15, the ham mer42 is released and strikes the firing pin 30 which, in turn, strikes andfires the cartridge in the chamber 29.

When the cartridge is fired, the slide 13, slide handle 14 and bolt 12move rearwardly and then forwardly to repeat the sequence of operationsdescribed in the preceding two paragraphs. The rifle will continue tofire automatically in the manner described as long as the triggerremains pulled and the ammunition holds out. When the trigger 15 isreleased and allowed to return to its usual position, the primary searnotch 45 of the hammer is engaged and held by the primary sear 38 of thetrigger while, at the same time, the secondary sear notch 46 is releasedby the secondary sear 40 in the manner previously described. The rifleis once again in its cocked and ready-to-fire condition.

The automatic rifle shown in the drawings is designed to be readilyassembled and disassembled, either in the shop or in the field. Allparts of the firing mechanism are securely mounted either on thereceiver 11 or on the trigger housing 34 as shown in FIGS. 3 and 4 ofthe drawings. As previously noted, the receiver 11 and the partsassociated therewith are inserted into the slot 26 of the stock 19 fromabove and the trigger housing 34 and the parts associated therewith areinserted into the slot 26 from below, the receiver and trigger housingbeing secured together by the hook-like elements 125 of the triggerguard 16 in the manner known in the art. The parts mounted on thereceiver 11 that are intended to cooperate with other parts mounted onthe trigger housing 34 are designed to mesh or mate togetherautomatically. as exemplified by the automatic engagement of thepositioner engaging stud 67 by the stud receiving slot 77 when thereceiver 11 and the trigger housing 34 are secured together. When thussecured together the receiver 11 and the trigger housing 34 comprise astructure referred to herein and in the claims as the frame of thefirearm.

The various parts of the firing mechanism are advantageously organizedinto sub-assemblies which are mounted either on the trigger housing 34or on the receiver 11. For example, the activator link positioner 73 andthe automatic fire activator link 76 comprise one such sub-assembly, andthe interrupter member 96 and the indexing and interrupter assemblyl02-l10 comprise another such sub-assembly, both mounted on the triggerhousing 34. The sub-assembly concept is particularly well exemplified bythe trigger, secondary sear and interrupter support member sub-assemblyshown in FIGS. 16, 17, and 18 in which the various parts are firstpivotally assembled on the assembly bushing 127 as shown best in FIG. 17before being pivotally mounted on the trigger housing 34 by means of thetrigger pivot 35 as shown in FIG. 16. In this embodiment, the pivot holeportion 128 of the trigger I5 is adapted to be received between the pairof downwardly extending pivot hole portions 129 of the support member96a, and the pivot hole portion 130 of the secondary sear 40a is adaptedto be received in the upper secondary sear receiving slot 131 formed inthe support member 96a and in the lower secondary sear receiving slot132 formed in the trigger 15. To assemble the parts the support memberspring 97 is placed in the spring receiving holes 133 and 134 formed inthe trigger l5 and in the support member 96a, respectively, and theassembly bushing 127 is inserted through the pivot hole 136 formed inone of the dependant pivot portions 129 of the support member 96a andthrough the adjacent trigger pivot hole 36 of the trigger 15. Thesecondary sear spring 41a is then inserted in the spring receiving hole138 formed in the trigger 15 and the pivot hole portion 130 of thesecondary sear 40a is inserted into the upper and lower secondary searreceiving slots 131 and 132. The assembly bushing 127 is then completelyinserted through the pivot hole 140 of the secondary sear and the pivotholes 36 and 136 of the trigger l5 and support member 96a as shown inFIG. 17. The resulting assembly is then mounted on the trigger housingas shown in FIG. 16.

We claim:

1. In an auto-loading firearm having a frame, a barrel secured to theframe, a bolt mounted for longitudinal travel in the frame behind thebarrel, an auto-loading mechanism connected to the bolt for moving thebolt from its forward closed position to its rearward open position andreturn when the firearm is fired, a hammer pivotally mounted on theframe, said hammer being formed with a primary sear notch and with asecondary sear notch, a trigger pivotally mounted on the frame, saidtrigger having a primary sear for engaging the primary sear notch of thehammer, a secondary sear pivotally mounted on the frame for engaging thesecondary sear notch of the hammer, a rocker arm pivotally mounted onthe frame, the rearward end of the pivoted rocker arm being movedupwardly when the bolt is at its forward closed position and being moveddownwardly when the bolt is moved to its rearward open position, saidupward and downward movement of the rocker arm alternately causing thesecondary soar to be disengaged from and permitting the secondary searto engage the secondary sear notch of the hammer, the improvement whichcomprises a firing mechanism capable of firing semi-automatically, fullyautomatically and in bursts of predetermined duration, said mechanismcomprising:

a secondary sear disengager and interrupter support member pivotallymounted on the frame, upward movement of the forward end of said pivotedsupport member causing the upper end of the secondary sear to moverearwardly out of engagement with the secondary sear notch of thehammer,

an indexing and interrupter assembly rotatably mounted on the forwardend of said support member, said assembly comprising an indexing ratchethaving a predetermined number of ratchet teeth and an interrupter dischaving at least one disengager arm contact surface and at least onedisengager arm receiving notch,

an indexing pawl pivotally mounted on the hammer, said pawl engaging theteeth of said indexing ratchet and causing said indexing and interrupterassembly to rotate one tooth at a time each time a cartridge is fired,

an activator link positioner pivotally mounted on the frame forlongitudinal movement to a rearwardmost, to an intermediate and to aforwardmost position,

an automatic fire activator link pivotally mounted on said activatorlink positioner, said activator link having a rocker arm engaging meansadapted to engage the rearward end of said rocker arm and a secondarysear disengager arm adapted to contact the interrupter disc of theindexing and interrupter assembly, said rocker arm engaging means andsaid secondary sear disengager arm being movable forwardly andrearwardly by corresponding movement of the activator link positionerand being movable upwardly and downwardly by corresponding movement ofsaid rocker arm when in engagement therewith, said secondary seardisengager arm moving the foreward end of said support member upwardlyto disengage said secondary sear when said disengager arm is movedforwardly and upwardly into contact with an arm contact surface of saidinterrupter disc,

said activator link positioner being moved to its rearwardmost positionto place the activator link at its semi-automatic fire position at whichthe rocker arm engaging means is out of engagement with the rearward endof the rocker arm and the disengager arm is out of position to contactthe interrupter disc of the indexing and interrupter assembly,

said activator link positioner being moved to its intermediate positionto place the activator link at its burst fire position at which therocker arm engaging means is in engagement with the rearward end of therocker arm and the forward end of the disengager arm is in position tocontact the arm contact surfaces and to enter the arm receiving notchesof the interrupter disc when the disengager arm is caused to moveupwardly by the rocker arm, and

said activator link positioner being moved to its forwardmost positionto place the activator link at its fully automatic fire position atwhich the rocker arm engaging means is in engagement with the rearwardend of the rocker arm and the forward end of the disengager arm is inposition to contact the arm contact surfaces of the interrupter disc andis forward of the position at which it can enter the arm receivingnotches of the interrupter disc when the disengager arm is caused tomove upwardly by the rocker arm.

2. The firearm according to claim 1 in which a manual movable firingmode selector is pivotally mounted on the frame, said selector beingconnected to the activator link positioner and being movable about itspivotal mounting to move said activator link positioner to itsrearwardmost, its intermediate and its forwardmost positions.

3. The firearm according to claim 1 in which the secondary seardisengager and interrupter support member is secured to the secondarysear, whereby upward movement of the forward end of said support membermoves the upper end of the secondary sear rearwardly out of engagementwith the secondary sear notch of the hammer.

4. The firearm according to claim 1 in which the secondary sear and thesecondary sear disengager. and interrupter support member areindependently pivotally mounted on the frame, in which said supportmember is formed with a secondary sear stop surface and in which saidsecondary sear is formed with a stop engaging lug, said stop engaginglug normally contacting said secondary sear stop surface, whereby upwardmovement of the forward end of said support member causes the upper endof the secondary sear to move rearwardly.

5. The firearm according to claim 1 in which the trigger is providedwith a support member lifting lug that normally is in contact with thesecondary sear disengager and interrupter support member, forwardmovement of the trigger causing the support member lifting lug to movethe forward end of said support member upwardly and thereby move theupper end of the secondary sear rearwardly out of engagement with thesecondary sear notch of the hammer.

6. The firearm according to claim 1 in which the trigger is providedwith an activator movement preventer lug that is adapted to move intoengagement with a first preventer receiving surface formed in theactivator link when the activator link is at its rearwardmost position,into engagement with a second preventer receiving surface formed in saidactivator link when said activator link is at its intermediate position,and into engagement with a third preventer receiving surface formed inthe activator link when said activator link is at its forwardmostposition.

7. The firearm according to claim 1 in which the interrupter disk isformed with at least one disengager arm receiving notch, and in whichthe indexing ratchet is formed with at least two ratchet teeth.

8. The firearm according to claim 1 in which the interrupter disk isformed with at least two disengager receiving notches and in which theindexing ratchet is formed with a number of ratchet teeth that is amultiple of the number of said disengager arm receiving notches.

9. The firearm according to claim 1 in which the indexing andinterrupter assembly is provided with a detent that releasably detainssaid assembly from further rotation after said assembly has been rotatedan angular distance equivalent to one ratchet tooth by the indexingpawl.

10. The firearm according to claim 1 in which the automatic fireactivator link is formed with a trigger pivot pin receiving slot that isadapted to engage the pivot pin on which the trigger is pivotallymounted when said activator link is at its rearwardmost position, saidpivot pin receiving slot being moved out of engagement with the saidpivot pin when the activator link is moved forwardly to its intermediateposition. a:

1. In an auto-loading firearm having a frame, a barrel secured to theframe, a bolt mounted for longitudinal travel in the frame behind thebarrel, an auto-loading mechanism connected to the bolt for moving thebolt from its forward closed position to its rearward open position andreturn when the firearm is fired, a hammer pivotally mounted on theframe, said hammer being formed with a primary sear notch and with asecondary sear notch, a trigger pivotally mounted on the frame, saidtrigger having a primary sear for engaging the primary sear notch of thehammer, a secondary sear pivotally mounted on the frame for engaging thesecondary sear notch of the hammer, a rocker arm pivotally mounted onthe frame, the rearward end of the pivoted rocker arm being movedupwardly when the bolt is at its forward closed position and being moveddownwardly when the bolt is moved to its rearward open position, saidupward and downward movement of the rocker arm alternately causing thesecondary sear to be disengaged from and permitting the secondary searto engage the secondary sear notch of the hammer, the improvement whichcomprises a firing mechanism capable of firing semiautomatically, fullyautomatically and in bursts of predetermined duration, said mechanismcomprising: a secondary sear disengager and interrupter support memberpivotally mounted on the frame, upward movement of the forward end ofsaid pivoted support member causing the upper end of the secondary searto move rearwardly out of engagement with the secondary sear notch ofthe hammer, an indexing and interrupter assembly rotatably mounted onthe forward end of said support member, said assembly comprising anindexing ratchet having a predetermined number of ratchet teeth and aninterrupter disc having at least one disengager arm contact surface andat least one disengager arm receiving notch, an indexing pawl pivotallymounted on the hammer, said pawl engaging the teeth of said indexingratchet and causing said indexing and interrupter assembly to rotate onetooth at a time each time a cartridge is fired, an activator linkpositioner pivotally mounted on the frame for longitudinal movement to arearwardmost, to an intermediate and to a forwardmost position, anautomatic fire activator link pivotally mounted on said activator linkpositioner, saiD activator link having a rocker arm engaging meansadapted to engage the rearward end of said rocker arm and a secondarysear disengager arm adapted to contact the interrupter disc of theindexing and interrupter assembly, said rocker arm engaging means andsaid secondary sear disengager arm being movable forwardly andrearwardly by corresponding movement of the activator link positionerand being movable upwardly and downwardly by corresponding movement ofsaid rocker arm when in engagement therewith, said secondary seardisengager arm moving the foreward end of said support member upwardlyto disengage said secondary sear when said disengager arm is movedforwardly and upwardly into contact with an arm contact surface of saidinterrupter disc, said activator link positioner being moved to itsrearwardmost position to place the activator link at its semi-automaticfire position at which the rocker arm engaging means is out ofengagement with the rearward end of the rocker arm and the disengagerarm is out of position to contact the interrupter disc of the indexingand interrupter assembly, said activator link positioner being moved toits intermediate position to place the activator link at its burst fireposition at which the rocker arm engaging means is in engagement withthe rearward end of the rocker arm and the forward end of the disengagerarm is in position to contact the arm contact surfaces and to enter thearm receiving notches of the interrupter disc when the disengager arm iscaused to move upwardly by the rocker arm, and said activator linkpositioner being moved to its forwardmost position to place theactivator link at its fully automatic fire position at which the rockerarm engaging means is in engagement with the rearward end of the rockerarm and the forward end of the disengager arm is in position to contactthe arm contact surfaces of the interrupter disc and is forward of theposition at which it can enter the arm receiving notches of theinterrupter disc when the disengager arm is caused to move upwardly bythe rocker arm.
 2. The firearm according to claim 1 in which a manualmovable firing mode selector is pivotally mounted on the frame, saidselector being connected to the activator link positioner and beingmovable about its pivotal mounting to move said activator linkpositioner to its rearwardmost, its intermediate and its forwardmostpositions.
 3. The firearm according to claim 1 in which the secondarysear disengager and interrupter support member is secured to thesecondary sear, whereby upward movement of the forward end of saidsupport member moves the upper end of the secondary sear rearwardly outof engagement with the secondary sear notch of the hammer.
 4. Thefirearm according to claim 1 in which the secondary sear and thesecondary sear disengager and interrupter support member areindependently pivotally mounted on the frame, in which said supportmember is formed with a secondary sear stop surface and in which saidsecondary sear is formed with a stop engaging lug, said stop engaginglug normally contacting said secondary sear stop surface, whereby upwardmovement of the forward end of said support member causes the upper endof the secondary sear to move rearwardly.
 5. The firearm according toclaim 1 in which the trigger is provided with a support member liftinglug that normally is in contact with the secondary sear disengager andinterrupter support member, forward movement of the trigger causing thesupport member lifting lug to move the forward end of said supportmember upwardly and thereby move the upper end of the secondary searrearwardly out of engagement with the secondary sear notch of thehammer.
 6. The firearm according to claim 1 in which the trigger isprovided with an activator movement preventer lug that is adapted tomove into engagement with a first preventer receiving surface formed inthe activator link when the activator link is at its rearwardmostposition, into engagement with a second preventer receiving surfaceformed in said activator link when said activator link is at itsintermediate position, and into engagement with a third preventerreceiving surface formed in the activator link when said activator linkis at its forwardmost position.
 7. The firearm according to claim 1 inwhich the interrupter disk is formed with at least one disengager armreceiving notch, and in which the indexing ratchet is formed with atleast two ratchet teeth.
 8. The firearm according to claim 1 in whichthe interrupter disk is formed with at least two disengager receivingnotches and in which the indexing ratchet is formed with a number ofratchet teeth that is a multiple of the number of said disengager armreceiving notches.
 9. The firearm according to claim 1 in which theindexing and interrupter assembly is provided with a detent thatreleasably detains said assembly from further rotation after saidassembly has been rotated an angular distance equivalent to one ratchettooth by the indexing pawl.
 10. The firearm according to claim 1 inwhich the automatic fire activator link is formed with a trigger pivotpin receiving slot that is adapted to engage the pivot pin on which thetrigger is pivotally mounted when said activator link is at itsrearwardmost position, said pivot pin receiving slot being moved out ofengagement with the said pivot pin when the activator link is movedforwardly to its intermediate position.